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Community and Q&A

Bathroom ventilation

user-2423385 | Posted in Energy Efficiency and Durability on

Ok..two baths one above another in a two story home. Top floor bath 70 square feet, bottom 45 square. I was thinking of running an Inline fan a few feet from the 1st floor exterior under a stairway next to the lower floor bath, piped for both bathrooms, running timer switches in parallel. The upstairs is a slanted ceiling so a standard fan will not work. In the interest of money I think a single fan would work well. I have a few questions and if you had any insight I thank you in advance.

1. Should I run rigid duct work in the conditioned spaces and then insulated flex in the attic to access the upstairs bath.
2. Is the plan on running the system top to bottom and exiting the house just above the sill plate a good idea?
3. Is running both fans at once going to drain the heat/cold from the house noticeably or would it be worth the extra couple hundred dollars to use separate fans to vent the bathrooms (money is an issue at the moment) and if so…is running the system down rather than up and out a viable idea as less holes in the roof is better as far as I’m concerned. Thanks much!!!

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  1. GBA Editor
    Martin Holladay | | #1

    Rigid duct (galvanized duct) is better than flex duct. In the attic, the galvanized duct can be (and should be) wrapped with duct insulation.

    Whether or not you want the exhaust fans controlled by a timer or a wall switch depends on the purpose the fans will fulfill. If you want the fans to remove bathroom odors and humidity associated with showers and baths, it's best to control the fans with a wall switch.

    If the fans are part of a mechanical ventilation system designed to provide your house with fresh air, then it may make sense to control one or both fans with a timer. Be careful that you don't over-ventilate your house, because there is always an energy penalty associated with any ventilation system.

    For more information, see Designing a Good Ventilation System.

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